New tunneling source follower with low 1/f noise and high voltage gain.

We have designed a tunneling source follower (TSF) for image sensors that achieves high voltage gain (A) and low 1/f noise simultaneously. The TSF is composed of N-P-N-N, especially the p-doped grounded area, which serves to amplify the insufficient tunneling current, allowing the source follower (SF) to utilize band-to-band tunneling (BTBT). Compared to thermionic emission, tunneling based structures contribute to increasing A through lower channel length modulation and lower body effect. As a result, TSF achieves a higher A (~ 1.0 V/V) than conventional SF (~ 0.9 V/V). Moreover, the n-doped channel makes the buried conductive channel farther from the interface, lowering the noise. The input-referred voltage noise spectral density (S) is approximately 10 times lower in TSF than that of in conventional SF. Therefore, our TSF can be a possible candidate for High A and low 1/f noise image sensors.